1. Field of the Invention
Embodiments of the present invention generally relate to wellbore operation. More particularly, the invention relates to a method of use and an apparatus for sealing around a tubular. Still more particularly, the invention relates to a seal assembly for use in a control head.
2. Description of the Related Art
Drilling a wellbore for hydrocarbons requires significant expenditures of manpower and equipment. Thus, constant advances are being sought to reduce any downtime of equipment and expedite any repairs that become necessary. Rotating equipment is particularly prone to maintenance as the drilling environment produces abrasive cuttings detrimental to the longevity of rotating seals, bearings, and packing elements.
In a typical drilling operation, a drill bit is attached to a string of drill pipe. Thereafter, a drive unit rotates the string of drill pipe through a drive member, referred to as a kelly as the string of drill pipe and drill bit are urged downward to form the wellbore. In some arrangements, a kelly is not used, thereby allowing the drive unit to attach directly to the drill pipe. The length of the wellbore is determined by the location of the hydrocarbon formations. In many instances, the formations produce gas or fluid pressure that may be a hazard to the drilling crew and equipment unless properly controlled.
Several components are used to control the gas or fluid pressure. Typically, one or more blow out preventers (BOP) are mounted to the well forming a BOP stack to seal the mouth of the well. Additionally, an annular BOP is used to selectively seal the lower portions of the well from a tubular body that allows the discharge of mud through the outflow line.
An example of a BOP is disclosed in U.S. Pat. No. 4,440,232. The BOP in '232 uses a spherical sealing element to seal the mouth of the well. The spherical sealing element is typically made from an elastomeric material and formed in a shape of a dome with a hole in the middle thereof wherein the inner diameter of the spherical sealing element is greater than an outer diameter of a tubular and greater than an outer diameter of a tubular joint. An upper end of the spherical sealing element is reinforced by a plurality of flanged steel inserts and a lower end of the spherical sealing element is supported by a movable tapered piston. In operation, fluid pressure wedges the tapered piston against the spherical sealing element, thus urging the spherical sealing element against the plurality of flanged steel inserts and causes the spherical sealing element to move radially outward into contact with the tubular to form a seal between the BOP and the tubular. Even though an effective seal is formed between the BOP and the tubular, the spherical element may be damaged as the tubular is rotated and tubular joints are stripped through a closed BOP. More specifically, as the spherical sealing element is urged against the plurality of flanged inserts, the sealing element tends to extrude under the noses of the flanged inserts where it is restricted from movement and forced into the path of the moving tool joint which results in damage to the spherical sealing element.
In many instances, a conventional rotating control head, also referred to as a rotating blow out preventor, is mounted above the BOP stack. An internal portion of the conventional rotating control head is designed to seal and rotate with the string of drill pipe. The internal portion typically includes an internal sealing element mounted on a plurality of bearings. The internal sealing element may consist of both a passive seal arrangement and an active seal arrangement. The active seal arrangement is hydraulically activated. Generally, a hydraulic circuit provides hydraulic fluid to the rotating control head. The hydraulic circuit typically includes a reservoir containing a supply of hydraulic fluid and a pump to communicate the hydraulic fluid from the reservoir to the rotating control head. As the hydraulic fluid enters the rotating control head, a pressure is created to energize the active seal arrangement. During the drilling operation, the string of drill pipe is axially and slidably forced through the rotating control head. The string of drill pipe is made up of individual drill pipes connected together at tool joints. The tool joints have a larger diameter than each individual drill pipe. In order to seal the mouth of the well, the active seal arrangement in the rotating control head must effectively maintain a seal around each drill pipe and the larger diameter joints between each drill pipe. However, the active seal arrangement in the conventional rotating control head has a tendency to leak at the seal as the string of drill pipe is axially forced through the rotating control head which may result in eventual failure of the rotating control head.
Additionally, as the string of drill pipe is axially and slidably forced through the rotating control head, the axial movement of the drill pipe causes wear and tear on the bearing and seal assembly and subsequently requires repair. Typically, the drill pipe or a portion thereof is pulled from the well and a crew goes below the drilling platform to manually release the bearing and seal assembly in the rotating control head. Thereafter, an air tugger in combination with a tool joint on the drill string is used to lift the bearing and seal assembly from the rotating control head. The bearing and seal assembly is replaced or reworked and thereafter the crew goes below the drilling platform to reattach the bearing and seal assembly into the rotating control head and operation is resumed. The process is time consuming and can be dangerous.
A need therefore exists for an improved active seal arrangement for a rotating control head. There is a further need for an active seal arrangement that can be efficiently removed from the rotating control for repair or replacement.